Tuning systems for radio and television receivers typically include a tunable RF stage for selecting the RF signal corresponding to a desired station or channel from a plurality of received RF signals, a tunable local oscillator for generating a local oscillator signal having a frequency corresponding to the desired station or channel and a mixer for heterodyning the selected RF signal with the local oscillator signal to produce an IF signal corresponding to the RF signal.
The local oscillator should be capable of generating a local oscillator signal of sufficient amplitude to reliably drive the mixer and provide an output impedance compatible with the input impedance of the mixer for efficient power transfer. In addition, the local oscillator should be arranged so that the mixer does not significantly interfere with the operation of the local oscillator. While it is possible to employ a separate buffer amplifier in conjunction with the local oscillator to provide these desired features, it is not economical to do so.